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On the subject of whether dinos could have had high active metabolic rates,
while at the same time retaining low *resting* metabolic rates, I feel that
obligitory bipedalism speaks against low resting metabolic rates.  If a
significant reason for "stable" leg configurations such as arthropods and
most "reptiles" is to avoid falling over when the nerves and muscles are too
cold to keep proper balance, then those (often early) oblig. bips. we are so
familiar with, would have been pretty warm all the time.

My temperature for the first hour or so on a cold morning is 94.2, and I
believe few coelophysis-shaped dinos couldn't have survived for long if
their running ability on waking up wasn't markedly better than mine!

Of course bigger dinos would have had more constant temperatures and been
less likely to have low resting metab. rates.


I wrote...
>> In reading Chris B's Deinosuchus paper in Nature, I noticed what a
>> specimen that _D_ skull is!

Chris Brochu replied:
>Uh... to quote the great Wann Langston, that skull is a "figment of the
>imagination."  The picture we published was intended to show size, NOT

Well, if we were selling casts, we wouldn't need to bother the customers
with all the details - after all we don't want to confuse them, do we! ;-)

>In the meantime, I have a little to say about it in the
>forthcoming alligatoroid phylogeny, but unless you're a hardcore clade
>runner, you won't care much.

Claderunner!  Hey - I like that a lot!  "Mission - to hunt down and retire
cladistry wherever it may be found".  Not quite what you meant, I know.

Sorry about trying to guess what you looked like - I thought it might be
rather jolly but I'm having second thought about that.

>Not sure what you mean by "kinked snout."  If you mean the notch between
>the maxilla and premax for the dentary fang(s), that's a plesiomorphic
>trait lost in a subset of alligatoroids.

That was the one I was thinking about.


Bill Adlam said:

>IMO the best terrestrial gas exchange system is the much-maligned
>tracheal system of insects.  In larger insects the flow is mostly
>unidirectional.  The tracheal system can deliver more oxygen than the
>vertebrate bloodstream, allowing higher metabolic rates.  And it does
>so with a minimum of water loss, allowing insects to live in the
>driest conditions.  It is also highly efficient, because air is much
>less viscous than blood.

Makes one wonder why birds etc never quite got that far.  Probably blood
carries more oxygen than air, and acts as a better internal cooling system.